To achieve a variably controllable reactance (e.g., capacitance) for an electronic device, arrays of switched elements have been combined into banks to provide a summed programmable reactance. To date, these arrays have been implemented with a single switching technology and device design. This uniformity simplifies the technology development and is a good solution for many applications, but in some applications, such as tunable filters in particular, large tuning ranges are desirable in combination with fine tuning resolution. Achieving both of these results with a single design can require that the devices each provide only a very small reactance shift. To make such a configuration cost-effective for substantial total reactance, the devices would necessarily need to be physically very small. Each device has overhead area driven by the design rules of the process, however, and thus the total array size would increase for a given total tuning range. In addition, the added interconnect area would also increase parasitics and lower overall ratio, and power handling often does not scale well with size. As a result, large arrays of very small devices may not be a practical solution.
One alternative can be to scale only a subset of devices in the array to provide fine tuning. When using an array of micro-electro-mechanical systems (MEMS) capacitors, for example, this configuration could provide a high performance solution, but such an arrangement would not be area efficient, as all capacitor bit values would have generally the same physical size. Even if the subset of devices were made physically smaller, having different MEMS mechanics makes achieving high process yield much more difficult.
As a result, it would be desirable for a configuration of an array of switched capacitors to provide a large tuning range in combination with a fine tuning resolution and to maintain high Q and/or linearity in the majority of the reactance, while avoiding the drawbacks of previous arrays configured to achieve such performance criteria.